Arc plasma generator with starter



T. A. BARR, JR.. ETAL 3,356,897

ARC PLASMA GENERATOR WITH STARTER Dec. 5, 1967 Filed Jan. 18, 1965 5Sheets-Sheet 1 v a I2 A :7 l5 \w I I8 Ila I20 I3&

FIG. I

SPARKING 1 CIRCUIT -LLZ/ HIGH 23o VOLTAGE 23 FIG. 2

Thomas A. Bcrr,J|'. Robert F. Mayo Thomas G. Roberts, INVENTORS:

T. A. BARR, JR.. ETAL ARC PLASF-ZA GENERATOR WITH STARTER Filed Jan. 18,1965 5 Sheets-Sheet 2 HIGH VOLTAGE 0.0. POWER SUPPLY I I U I r SI \24C II I SOLENOID f #25 i 26A 28 0 I l I F STARTER I \L I: I A II I I I I 27i K I 24b F r l. "I

I I m a I A) I L HI SC-LENOID HIGH VOLTAGE 0.0 POWER SUPPLY Thomas A.Borr,J|:

Robert F. Mayo Thomas G. Roberts,

INVENTORS. Z y

WE M 4 Dec. 5, 1967 T. A. BARR, JR, ETAL 3,355,897

I ARC PLASMA GENERATOR WITH STARTER 7 Filed Jan. 18, 1965 5 Sheets-SheetHIGH VOLTAGE D.C. POWER SUPPLY SOLENOID T] I kzgA 7 s HIGH VOLTAGE 0.0POWER SUPPLY SOLENOID Thgmas A. Burr,dr.

R0 err F. Mayo 7 FIG-6 Thomas G.Roberfs,

1NVENTORS.

United States Patent 3,356,897 ARC PLASMA GENERATOR WITH STARTER ThomasA. Barr, Jr., Robert F. Mayo, and Thomas G. Roberts, Huntsville, Ala.,assignors to the United States of America as represented by theSecretary of the Army Filed Jan. 18, 1965, Ser. No. 426,453 2 Claims.(Cl. 315-238) ABSTRACT OF THE DISCLOSURE An arc plasma generator with aspark-plug type starter. The starter has a vaporizable dielectricbetween its electrodes, and injects vapor from the dielectric betweenthe arc electrodes of the generator. This vapor allows an arc to bereadily struck between the electrodes of the generator.

The invention described herein may be manufactured and used by or forthe Government for governmental purposes without the payment of anyroyalty thereon.

This invention relates to an arc plasma generator starter which issimple in nature and inexpensive.

Arc plasma generators are finding extensive use now in various aerospaceresearch projects. An arc plasma can provide a high temperature, highvelocity flow which is useful for testing missile nosecones, or may beemployed for flame plating. The starting, or ignition of arc plasmas inprior art devices has been difficult.

An object 'of the present invention is to overcome the above difliculty.

"Another object of the invention is to provide an inexpensive arc plasmagenerator starter.

A further object is to provide an arc plasma generator starter which issimple to construct.

A still further object is to provide an arc plasma generator starterwhich may be accurately timed in operation.

Yet another object is to provide means whereby a plurality arc plasmagenerator starters may be accurately and simultaneously activated.

Many are plasma generators operate in a high vacuum and some means mustbe provided to form a conductive path through the vacuum before an arccan be established. In the past, this has been done by any one ofseveral different ways. A high voltage, as from a Tesla coil, may beused to cause a spark discharge within the arc plasma chamber, whichdischarge provides a conductive medium through which the arc plasma maybe established and maintained.

This scheme has the disadvantage that the high voltage from the Teslacoil can damage the insulators of the arc plasma chamber and mayeventually allow conductive paths to form through the insulators.

Other ways in which the arc plasma may be started are by the use of anexploding wire or cap within the arc chamber or by the use of a piece ofsteel wool between the arc electrodes to provide a low resistivity pathfor starting. Each of these ways has the disadvantage of requiringmanual reloading after each starting, and they are somewhat diificult tocontrol in time. The present invention requires only occasionalreloading, can be accurately timed and does not harm the arc chamberinsulators.

Basically, the invention is a starter for an arc plasma generator, whichstarter employs the ablation of a dielectric plastic by a high voltagespark-discharge to produce a small-scale plasma discharge.

The invention may be understood by reference to the drawings, in whichthe same numerals are used to designate the same parts appearing indifferent figures wherein:

FIGURE 1 is a view, partly in section, of the starter in accordance withthe invention;

' ing a center electrode 11 and center insulator 12 which extends beyondthe threaded metal body 13 of the plug. The normal ground electrode (notshown) of the plug is ground or filed off and a plastic insert 14 isinserted around the center insulator 12. The numeral 12a designates theexterior extension of the center insulator I2, and 11a is the exteriorextension of center electrode 11, to which high voltage lead 15 withinsulating boot 15a is connected. The arc plasma generator metal housingwall is member 16, and member 17 is a noncorroding metal gasket insertedbetween the insert 14 and the bottom of a bore in which body 13 of thestarter plug is screwed. A bore 18 passes between the electrode 11 andthe interior of the housing 16. The insert 14, in the specificembodiment, is made of Lucite, but many other substances would beproper. Polyethylene or other linear polymers could be used, as well asTeflon and other flurocarbon polymers. Other polymers or substances maybe used, the requirements being: a dielectric which does not shatterreadily under the electrical or other stresses'developed in the starter,which is readily vaporizable by a spark discharge and which leaves nosignificant ash upon vaporization. Gasket 17 may be brass, copper,stainless steel, tantalum or some other noncorroding metal. The gasketis not absolutely necessary, but is convenient because it prevents wearon housing 16.

FIGURE 2 shows the spark plug assembly in place in the housing 16, withthe set up of the arc plasma generator shown. The are plasma generatoris known in the artv and consists of an anode 19 and a cathode 16 (thehousing) surrounded by focusing electromagnets 21. Insulator 22separates the electrodes 19 and 16. A high voltage from high voltagesupply 23 is applied between the electrodes but is ordinarilyinsufiicient to start an arc therebetween. High voltage supply 23includes a high voltage terminal 23a connected to cathode 19, and aground (negative) terminal 231) connected to housing member 16 (theanode of the generator). A sparking circuit 24, with a high voltageterminal 24a and a ground (negative) terminal 24 has its high voltageterminal connected to high voltage lead 15 by lead 27, and its groundterminal connected to housing member 16. The details of circuit 24 areshown in the dotted line box labeled 24 in FIGURE 3.

FIGURE 3 shows a high voltage supply 240 connected to a solenoidoperated switch S When in the position as shown, S allows capacitor C tocharge through conductor 25 and conductor 26. When moved by solenoid 29through insulator 29a to its other position, switch S allows thecapacitor C to discharge through the spark lug 10 by way of conductor 28and conductor 27. The inductance L acts as a choke and prevents a highvoltage surge from appearing on the ground conductor 26 as the capacitorC discharges Switch S is a safety shorting switch for C and is normallyclosed when the device is not in use, and normally open when the deviceis in use. Terminals 24a and 24b correspond to like designated terminalsin FIGURE 2. FIGURE 3 is drawn to show two spark plugs connected to thefiring circuit, but obviously one, or more than two spark plugs could beconnected to be fired simultaneously. With the arrangement as shown, theplugs are fired at substantially the same instant.

Referring again to FIGURE 2, Whenthe spark plug fires, a portion of theplastic insert 14 is ablated and discharged as a plasma through thepassage 18 into the interior of the housing 16. This plasma increasesthe conductivity of the space between the anode 19 and cathode 16, andallows an arc to ignite between them. Once such are is started, the highvoltage supply 23 is of sufiicient voltage to maintain the arc.

FIGURE 4 shows a modified form of FIGURE. 1, but with a thyratron beingused to complete the discharge circuit for the capacitor C. Operation ofthe FIGURE 4 system is the same as that of FIGURE 3, except that switchS is ganged to switch S but is so arranged that S closes after S breaksbut before it can make the conductor 28 contact. This last contact for Scould be omitted in this embodiment. The closure of S applies voltagefrom battery B to the thyratron 30 to cause it to conduct.

FIGURE shows a further modified form of the basic circuit of FIGURE 3.Capacitor C is charged through conductors 25 and 31 and, when switch Sis operated from right to left, discharges through conductors 25 and 32.Inductor L acts as a choke to prevent a high voltage from appearing onconductor 33 when C discharges. The operation of the circuit isotherwise similar to the FIG- URE 3 circuit.

FIGURE 6 shows a modified form of FIGURE 5 in which a thyratron 30' isused as a switch for applying the high voltage to the starters. Theoperation of the circuit is substantially the same as that of FIGURE 5,except that switch S is ganged to switch S and makes contact afterswitch S opens but before S can make with its alternate contact. Ifdesired, such alternate contact could be omitted. When 8;; makescontact, voltage from battery B is applied to the grid of 30' and thethyratron conducts, allowing discharge of capacitor C.

In ach of the embodiments of FIGURES 3, 4, 5 and 6, it should be notedthat both electrodes of the spark plugs are at ground potential duringthe charging of capacitor C, except for the small voltage developedacross L or L during charging, such voltage being due to the IR dropacross the finite resistances of the inductors.

While specific embodiments of the invention have been disclosed, otherembodiments may be obvious to one skilled in the art.

While a modified automobile spark plug has been specifically described,other types of sparking plugs may be used, if the requiredspecifications are met.

The high voltage power supplies 23 and 24 have been shown as separate,but could obviously be tapped from the same high voltage supply source.Also, the voltage of the battery B could be tapped (with, for example,,avoltage divider) from the same source as 23 and 24. If desired, acurrent limiter for the charging current of C could be provided, in anyone of several known ways.

Solenoid 27 could be electrically, mechanically, hydraulically,pneumatically or manually operated to activate rod 29, and no specificmeans is shown for its operation.

Thyratrons 30 and 30 could be fired by a separate accurately timeddevice (not shown), if desired.

While a specific use has been described for this starter, it may findother uses, such as a blasting cap for explosives, or a Vernier rocketfor a space craft. The discharge from the starter could be used to causea circuit interruption in response to high voltage surge on the starter,and could be used as a circuit break and/or surge protector.

We claim:

1. An arc plasma generator having a housing with a first space therein;a centrally disposed electrode penetrating said space, but insulatedfrom said housing; a first high voltage source having a first groundterminal, connected to said housing and a first high voltage terminal,connected to said electrode, a starting device having an outer electrodewith a second space therewithin, and an inner electrode penetrating saidsecond space, but insulated from said outer electrode; said otherelectrode connected to said housing, with a passageway between saidspaces; a second high voltage source having a second ground terminal,connected to said housing and a second high voltage terminal, connectedto said inner electrode.

2. The starter of claim 1 in which the electrodes of said sparkingdevice comprise a first rod shaped electrode and a second coaxialcylindrical electrode surrounding said first electrode and in which saiddielectric surrounds one end of said first electrode, except for acoaxial perforation of less diameter than the first electrode.

References Cited UNITED STATES PATENTS 2,093,848 9/1937 Randolph et al.3l3l30 X 2,125,035 7/1938 Smits 315-209 2,392,192 1/ 1946 Robinson315-2-09 2,900,547 8/1959 Engel 313- 3,004,184 10/1961 Deans 313-131 X3,049,644 8/1962 Bowlus et al. 315--209 3,287,590 11/1966 Andre 313-JOHN W. HUCKERT, Primary Examiner.

A. J. JAMES, Assistant Examiner.

1. AN ARC PLASMA GENERATOR HAVING A HOUSING WITH A FIRST SPACE THEREIN;A CENTRALLY DISPOSED ELECTRODE PENETRATING SAID SPACE, BUT INSULATEDFROM SAID HOUSING; A FIRST HIGH VOLTAGE SOURCE HAVING A FIRST GROUNDTERMINAL, CONNECTED TO SAID HOUSING AND A FIRST HIGH VOLTAGE TERMINAL,CONNECTED TO SAID ELECTRODE, A STARTING DEVICE HAVING AN OUTER ELECTRODEWITH A SECOND SPACE THEREWITH, AND AN INNER ELECTRODE PENETRATING SAIDSECOND SPACE, BUT INSULATED FROM SAID OUTER ELECTRODE; SAID OTHERELECTRODE CONNECTED TO SAID HOUSING, WITH A PASSAGEWAY BETWEEN SAIDSPACES; A SECOND HIGH VOLTAGE SOURCE HAVING A SECOND GROUND TERMINAL,CONNECTED TO SAID HOUSING AND A SECOND HIGH VOLTAGE TERMINAL, CONNECTEDTO SAID INNER ELECTRODE.